1. Field of the Invention
This invention relates to a solenoid-type valve actuator for an internal combustion engine, for opening and closing a valve by two electromagnets.
2. Description of the Prior Art
Conventionally, a solenoid-type valve actuator of the above-mentioned kind has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 11-126715. The solenoid-type valve actuator, which opens and closes an intake valve, includes an armature arranged between two electromagnets, and upper and lower shafts integrally formed with the armature in a manner extending upward and downward, respectively, through the respective electromagnets. The armature is connected to the intake valve via the lower shaft, and opens and closes the intake valve by performing reciprocating motion caused by energization and deenergization of the two electromagnets. In this reciprocating motion of the armature, each of the shafts reciprocates while being guided by a guide hole formed in a yoke of a corresponding one of the electromagnets.
In the solenoid-type valve actuator constructed as above, however, high machining accuracy is required to form the guide holes for guiding the reciprocating motion of the shafts in the yokes of the respective electromagnets, which results in an increase in manufacturing costs of the valve actuator. Further, it is desirable to reduce sliding resistance between the shafts and the yokes with a view to improving response of the intake valve as well as to reducing power consumption of the electromagnets. To attain the reduction of the sliding resistance, if bearings, for instance, are employed, this results in a further increase in the manufacturing costs of the solenoid-type valve actuator.
It is an object of the invention to provide a solenoid-type valve actuator for an internal combustion engine, having an inexpensive and simple construction which is capable of maintaining stability of operation of a valve and at the same time reducing sliding resistance exhibited against the operation of the valve, thereby achieving improved response of the valve and reduced power consumption of electromagnets.
To attain the above object, the present invention provides a solenoid-type valve actuator for an internal combustion engine, for electromagnetically opening and closing a valve, comprising:
two electromagnets arranged in a manner opposed to each other with a space therebetween;
an armature arranged between the two electromagnets, for reciprocating motion by energization and deenergization of the two electromagnets;
two shafts projecting from respective opposite sides of the armature and extending through the two electromagnets, respectively, one of the shafts being connected to the valve; and
two shaft guides arranged in at least one of the two electromagnets in a line along a direction of the reciprocating motion of the armature, for guiding a reciprocating motion of at least one of the two shafts performed according to the reciprocating motion of the armature.
According to this solenoid-type valve actuator for an internal combustion engine, the armature is caused to reciprocate by energization and deenergization of the two electromagnets, whereby the valve is opened and closed by the shaft connected thereto. During this reciprocating motion of the armature, the at least one of the shafts sliding through the electromagnet having the two shaft guides disposed therein performs reciprocating motion while being guided by the two shaft guides. Since the shaft guides are arranged in a line along the direction of the reciprocating motion of the armature, differently from a case in which one shaft is guided by a single shaft guide or in which a yoke is used for guiding a shaft, it is possible to reduce the contact area between the shaft guides and the shaft while maintaining the same total length of the two shaft guides as that of the single shaft guide and that of the yoke. As a result, the shaft can be supported in a radially stable fashion, which makes it possible to maintain stability of the operation of the valve. Further, since the sliding resistance exhibited against the operation of the valve can be reduced, it is possible to improve response of the valve as well as to reduce power consumption of the electromagnets. In addition, it is possible to enhance accuracy in the opening and closing control of the valve. Moreover, compared with the prior art in which a guide hole is formed through a yoke of the electromagnet, the present embodiment can achieve the above advantageous effects by a more inexpensive and simple construction, i.e. simply by arranging the two shaft guides in a line in the direction of the reciprocating motion of the valve.
Preferably, the two shaft guides are arranged in a line along the direction of the reciprocating motion of the armature with a space provided therebetween.
Preferably, at least one of the two shaft guides is formed with a contact surface for contact with the at least one of the two shafts and a non-contact surface.
According to these preferred embodiments, it is possible to reduce the contact area between the shaft guides and the shaft.
More preferably, the two shaft guides are each formed with a contact surface for contact with an associated one of the two shafts, and a non-contact surface, and a ratio of a length of each contact surface in the direction of the reciprocating motion of the armature to a total length of the two shaft guides in the direction of the reciprocating motion is preset to a value of approximately xc2xc.
According to this preferred embodiment, it is possible to reduce sliding resistance between the shaft and the shaft guide, and at the same time maintain durability of the solenoid-type valve actuator.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.